It is known to provide an electric lamp which includes a reflector, a base such as a metal base shell attached to the reflector, and a light source positioned within the reflector and electrically connected to the base. For example, a conventional PAR lamp includes a molded glass reflector having the general form of a dished portion leading to a neck portion which is formed around the axis of the reflector. Typically, at least two holes are formed in the neck portion to allow electrical connection to a light source positioned within the reflector. In particular, lead wires extend from a lamp positioned within the reflector. The lead wire extend through respective holes in the neck portion. Such lead wires are mechanically and electrically attached to a metal base shell which has been attached to the neck portion of the reflector. Typically, the base shell is a brass base shell which is threaded for screwing into a mating electrical socket in a conventional manner.
When providing electric lamps of this type, it is essential that the metal base shell be firmly attached to the neck portion of the reflector. For example, when a completed lamp is placed in use it may be threaded into a socket with excessive vigor causing the threads of the lamp and the threads of the socket to bind. Further, during use the threaded base shell may be subjected to corrosion, dirt, temperature cycling and the like that may also act to bind the threads. In such instances, when it is necessary to replace the lamp, the bound threads will require an undesirably excessive unthreading force. Depending upon the extent to which the threads are bound in the socket, in some instances such excessive unthreading force may cause the metal base shell to be separated from the reflector rather than cause the lamp to be unscrewed from the socket. When this occurs, removal of the lamp from the socket becomes very difficult. In addition the electrical connections and sharp and/or torn edges of the metal base shell will be exposed which will cause a potentially hazardous situation including the possibility of fire and injury to the user.
Efforts have been made to firmly secure the neck portion of the reflector to the metal base shell. For example, in PAR lamps it is known to secure the metal base shell to the glass reflector using either an adhesive or mechanical means. Although adhesives are effective, they must withstand high temperatures, and such adhesives tend to be expensive. Another disadvantage is that such adhesives are typically cured at high temperatures, and this tends to discolor the conventional brass metal base shell. Alternatively, a nickel plated brass base shell may be used to eliminate such discoloration. However, nickel plated brass base shells tend to be more costly and are more difficult to work with using an automated system than are brass base shells. In fact, when nickel plated brass base shells are provided hand assembly operations are favored.
Mechanical assembly of lamps such as PAR lamps is relatively inexpensive and automation friendly, but is more difficult to implement reliably. For example, a conventional PAR lamp is formed with two peen holes by pressing a glass gob between two mold faces. In particular, a glass gob is dropped into a female mold cavity, and a male mold face is pressed therein to form the reflector. Two slides each of which include a peen pin are brought in from opposite sides of the mold apparatus to plunge peen holes into the reflector neck portion. Such peen pins and therefore the peen holes are diametrically located. When the reflector is removed from the female mold, the threaded metal base shell is attached to the neck portion by pushing the metal base shell all the way down onto the neck portion. Respective portions of the metal base shell, referred to as peens, are then pressed into the peen holes provided in the neck portion of the reflector using a convectional peening tool. Typically, the neck portion is formed with a slope so as to be readily removable from the female mold. Due to a slight interference between the inside diameter of the metal base shell and the largest diameter of the neck portion of the glass reflector, the metal will be in tension when the base is pushed all the way down onto the neck portion. Such tension serves to hold the metal base shell in place during the peening operation. However, if the metal base shell is not properly pushed very tightly all the way down against a seating ledge of the reflector, there will be a tendency for the metal base shell to move along the axis of the neck portion before and/or during the peening operation. Similarly, if the metal base shell and/or neck portion are not properly toleranced to provide the required metal tension, there may be a further tendency for the metal base shell to move along the axis of the neck portion. Such movement of the metal base shell will adversely affect the interface between the peens and the peen holes and provide an inadequate attachment between the metal base shell and neck portion. Further problems may result from the nature of the pressing operation. For example, the peening operation provides a dilemma in that excessive pressing by the peening tool will fracture the glass reflector and possibly tear the metal of the metal base shell, and under pressing will prevent the peens from being sufficiently pressed into the peen holes to securely attach the metal base shell to the reflector. Potential problems exist even when the correct amount of pressure is applied. For example, typically the two peen holes are positioned diametrically, and such configuration provides an axis for the peens and therefore the metal base shell to pivot about relative to the reflector. When this occurs, the remaining portion of the metal base shell can then swivel or lift from the outer peripheral surface of the neck portion of the reflector. As a practical matter, this condition causes the peens to rock back and forth, thereby loosening the peens and/or causing them to rock out of the peen holes. This problem is compounded if the metal base shell is not properly seated and pressed squarely onto the neck portion since the metal base shell may be deformed during such inaccurate seating. When such a condition occurs, the metal base shell will flex around the neck portion of the reflector, and an undesirably shorter peen may be formed by the peening tool. When the peening tool is removed, the metal base shell will tend to flex back thereby lifting the shorter peen(s) further away from and possibly out of the peen hole(s). In addition to the foregoing, rocking of the metal base shell may tend to round off the peens which will cause the peens to slip from the peen holes. In those instances where there is a tendency for the peens to be removed from the peen holes, regardless of the cause, the metal base shell will break free from the neck portion of the reflector.
Efforts to provide lamps with more than two peens and respective peen holes to improve the attachment of the metal base shell to the reflector have been directed to embodiments wherein the holes are equally spaced around the metal base shell and are radially aligned; that is, the axis of each hole is extended towards the axis of the metal base shell and neck portion of the reflector. Production of such a lamp has not been practical due to the high cost of retooling. In particular, in present tool design wherein the neck portion of the reflector is provided with two diametrical peens, the space provided for producing the two peens, which are separated by 180.degree., is already occupied by the mechanism which retracts the current peen pins which effect the diametrically located opposing peens. Since there is no room for additional peen tools, the cost of providing a lamp with more than two peens is enormous.
Another problem which occurs during the manufacture of such a PAR lamp is that due to the limited space between the rim of the metal base shell and the first thread thereof, it is necessary for the edge of the peen hole to be tangent to the seating plane of the metal base shell. This presents the possibility of tearing through the rim of the metal base shell during the peening operation. Any such tearing completely destroys the strength of the metal base shell. Lamps damaged in this manner can not be shipped or sold under any circumstances.